In-mold coating processes have been developed to improve the quality of the surface of a molded article after the curing of the article in a compression mold has been substantially completed. In the compression molding process, two or more shaped mold elements cooperate to define a mold cavity. A molding composition typically comprising a polymerizable thermosetting or thermoplastic resin and fibrous reinforcing material and usually fillers, catalysts, mold release agents, and other reagents is introduced into the mold cavity between the mold surfaces. The shaped mold elements are brought together to spread the molding composition throughout the mold cavity and to confine the molding composition until curing is essentially completed. The molded article is then coated within the mold.
A process for molding and coating a substrate in a mold is described in U.S. Pat. No. 4,668,460, which is incorporated herein by reference. This process typically involves injecting a resin compound into a shaped mold, compressing the mold to form the desired substrate, applying heat to cure the resin, and injecting a coating composition into the mold to coat the substrate. U.S. Pat. No. 4,668,460 describes a method of coating the substrate in which the coating composition is injected into the closed, pressurized mold cavity at a high pressure and is forced over the surface of and compresses the substrate.
The ability of the coating to adequately cover the substrate depends in part on the viscosity of the coating composition. For example, application of a coating composition to the surface of a flexible thermoplastic substrate can be improved when the viscosity of the coating is relatively low, i.e., 15000 cps or less at room temperature.
Therefore, it is an object of the present invention to provide a two-component urethane coating having reduced viscosity and improved surface coverage properties.
Another object of this invention is to provide a cured molded thermoplastic part with an adherent in-mold coating.
These and other objects and advantages of the present invention will become more apparent to those skilled in the art from the following detailed description of the invention.